Observer based current control of single-phase inverter in DQ rotating frame

A modified current control scheme in D-Q rotating frame for single-phase inverters is presented in this paper to provide zero steady state error at fundamental frequency as well as waveform fidelity. The new procedure uses tuned observers to transform the physical quantities like "current" to real and imaginary values in stationary frame. The rotation matrix is used to transform from stationary frame to synchronous frame so that the transformed current values in steady state become DC variables in DQ frame. The controller design is similar to conventional DC/DC converters. The concept is validated by simulation in MATLAB and realized using FPGA EP1C3T100C7. The experimental results are provided for current control of single-phase inverters supplying R, RL and RC loads. The voltage control loop for UPS applications is also discussed in the paper.